1. Field of the Invention
The present invention relates generally to a variable valve timing arrangement for an internal combustion engine and more specifically to a rocker arm construction for such an arrangement.
2. Description of the Prior Art
JP-A-63-167016 and JP-A-63-57805 disclosed rocker arm arrangements which include a first rocker arm which is arranged to cooperate with a low speed cam and a second rocker arm which cooperates with a high speed cam. The two rocker arms pivotally mounted on a common rocker arm shaft.
A hydraulically operated connection device which enables the first and second rocker arms to be selectively locked together, comprises a set of plunger bores which are formed in the rocker arms in a manner to be parallel with and at a predetermined distance from the axis of the shaft about which the arms are commonly pivotal. By applying a hydraulic pressure to the end or ends of the plungers reciprocally disposed in the bores, the plungers can be induced to move axially within their bores and induce the situation wherein two of the plungers will partially enter an adjacent bore and lock the two arms together.
However, this arrangment has suffered from the drawbacks that at least one rocker arm shaft must be provided on the cylinder head to support the rocker arms in position. This of course consumes valuable space and increases the number of parts which must be disposed on the cylinder head. In addition as the rocker arms are actually supported by the rocker arm shaft, it is subject to relatively large moments of force and thus must be relatively robust and the cylinder head provided with suitable webs to facilitate suitable mounting of the same.
Further, as the axis about which the rocker arms are pivoted are fixed with the rocker arm shaft, it is necessary to provide adjust screws for adjusting the valve clearances at the valve engaging ends of the rocker arms. This provision increases the mass of the arms and therefore the moments produced by the same. This tends to reduce engine response at high engine speeds.